In order to solve the problems of the above-mentioned vacuum pump 100, a vacuum pump, which is disclosed in Korean Patent No. 393434 (which corresponds to U.S. Pat. No. 6,394,760), is shown in FIG. 2. According to the cited document, the vacuum pump 200 includes a plurality of nozzles 202, 203, 204, and 205 which are arranged in series and have slots 207, 208, and 209 between the nozzles, and valve members 210 which are provided between the nozzles and close or open communication holes 206 formed in walls of the respective nozzles. Further, a coupling means for coupling each nozzle to an integrated, rotationally symmetric nozzle body 201 is provided on each nozzle. The vacuum pump 200 is directly accommodated in a housing H of another device, and is operated by compressed air which sequentially passes through the nozzles at high speed, thus creating negative pressure in the internal space S of the housing H. However, the vacuum pump 200 is problematic in that connection parts between the nozzles are apt to be deformed (bent or twisted) or separated from each other by external force or shocks.
Another conventional vacuum pump, which was proposed by the applicant of this invention in order to overcome the drawback of the above vacuum pump 200, and is disclosed in Korean U.M. Registration No. 365830, is shown in FIGS. 3 and 4. According to the cited document, the vacuum pump 300 includes a cylindrical nozzle body 301, a cover 305, and a flexible valve member 307. An opening 302 is formed at a predetermined position in the nozzle body, and a plurality of nozzles 303 and 304 is installed in the nozzle body. The cover closes the opening 302. The valve member is provided to open or close several holes 306 which are formed in a wall of the nozzle body 301. In the vacuum pump 300, each nozzle is safely held in the cylindrical nozzle body. However, the vacuum pump is problematic in that the number of required parts is very high, so that it is difficult and inconvenient to produce and assemble the vacuum pump, and the vacuum pump is weakly resistant to external shocks. Further, the valve member must be skillfully designed such that it is secured to an edge of the opening of the nozzle body and extends along the holes. Thus, it is very difficult to manufacture and mount the valve member.